Abstract: An electronic device for indicating an abnormal condition in a rotatable member. A typical use for such a device would be for the detection of a low pressure condition in a tire on a vehicle. In the preferred form for this typical use, a reflecting surface, such as a mirror, is affixed to the wheel and associated with a pressure sensitive device. A light source reflects light off the mirror upon each revolution of the tire which is received by a photo-transistor. A timing device in the form of a retriggerable monostable multivibrator is triggered by the photo-transistor and puts out a high signal for a predetermined period of time. As long as the timing device receives triggering signals at time intervals less than that predetermined period of time, the output of the timing device will remain high and no alarm will be given.

Abstract: A device for providing an optical indication of the pressure condition in a pressurized member, such as a pneumatic tire. A housing having a window therein carries a reflective surface, such as a mirror, which is mounted on a movable flap. One end of a plunger pin holds the mirror in alignment with the window with the other end of the pin resting on a diaphragm assembly which communicates with the internal pressure of the member. Light from a light source is directed in the window and under normal pressure conditions will be reflected by the mirror. If the internal pressure of the member drops below a predetermined value, the diaphragm will retract dropping the pin thereby moving the mirror out of alignment with the light source. The absence of reflected light is thus indicative of a low pressure condition and corrective measures can be taken.

Abstract: An electronic alarm circuit indicates an abnormal pressure condition in a pneumatic tire on a vehicle. The circuit includes an indicator, either in the form of a light or sound buzzer, or both, which can transmit two distinguishable signals, one indicating the presence of an abnormal pressure condition and the other to test the circuit. An actuation circuit includes a normally open pressure switch which communicates with the internal pressure of the tire and closes upon the detection of the abnormal pressure to activate the indicator. The actuation circuit also includes a resistance connected across the pressure switch to provide a path for electrical current when the switch is open to provide the test signal, as may be desired.